The present invention relates to a carriage moving device and, more particularly, to a chain drive type carriage reciprocating device which reciprocates a carriage such as a document table of a copying machine carrying a copy document.
One type of electrophotographic copying machine is operated in a manner that a document table carrying an original document reciprocates so as to expose an image of the original document on a photoreceptor through an optical system.
A document table reciprocating device of the chain delivery type as shown in FIG. 1 has been proposed for use in the above copying machine. For example, the above document table reciprocating device is disclosed in U.S. Pat. No. 4,332,458, issued on June 1, 1982, by Lionel B. Hoffman, entitled "TABLE TOP COPY MACHINE".
In the type of electrophotographic copying machine in which the document table carrying the original document is reciprocated, as shown in FIG. 1, the document table (not shown) is driven by a motor through a driving chain 3 and sprockets 1 and 2.
The driving chain 3 is coupled around the sprockets 1 and 2 which are disposed near to each end of the path of the document table. A drive pin (or roller) 4 is coupled to the driving chain 3. A plate 5 is secured at a desired position to the bottom of the document table and has a hole 6. The hole 6 is in a rectangular shape having semicircular ends. The drive pin 4 is inserted within the hole 6 of the plate 5 as shown in FIG. 2 and vertically movable inside the hole 6. The plate 5 with the pin 4 is moved in the horizontal directions of the sprockets 1 and 2 along the driving chain 3. One of the sprockets 1 and 2 is coaxially mounted on the drive shaft of a motor. As the motor turns, the driving chain 3 is driven around the sprockets 1 and 2. The drive pin 4 pulls the plate 5 connected to the document table along the driving chain 3. As the drive pin 4 travels around either sprockets 1 or 2, the document table movement is reversed to achieve a continuous reciprocating motion. Thus, the document table can perform the reciprocating movements.
The turning points of the drive pin 4 are denoted by points a and b on the sprockets 1 and 2 as shown in FIG. 1.
As described above, while the copying operation of the copying machine is carried out, the driving chain 3 is driven in the arrow direction "L" by the motor so as to perform the reciprocating movement of the document table.
On the other hand, when the copying operation is not carried out and the driving chain 3 is not driven by the motor, the document table can be manually moved. However, even when the document table is manually moved and the drive pin 4 with the plate 5 connected to the document table is reached at the turning point a or b of the sprockets 1 and 2, the drive pin 4 is locked so that the drive pin 4 is stopped moving at the turning points a or b. After the drive pin 4 is locked at the turning point a or b, the document table cannot be manually moved.
The above problem will be described with reference to FIGS. 3 and 4 when the drive pin 4 is stopped moving at the turning point b.
It is assumed that the drive pin 4 is set at the upper line of the driving chain 3 as shown in FIG. 1 and the document table is manually moved in the direction of the sprocket 1 (in the arrow direction "R") without driving the driving chain 3 by the motor.
When the drive pin 4 arrives at the point c short of the turning point b according to the movement of the plate 5, as shown in FIG. 4(A), a force Fh in a horizontal direction from the plate 5 at the point c is divided into a force component Ft in a tangential direction of the sprocket and force component Fr in a radius direction of the sprocket, so that the drive pin 4 is rotated and moved by means of a moment produced by the force component Ft. Accordingly, the drive pin 4 reaches the turning point b passing through the point c.
On the other hand, it is assumed that the drive pin 4 is set at the lower line of the driving chain 3 and the document table is manually moved in the direction the sprocket 1 (or in the arrow direction "R").
When the drive pin 4 arrives at the point d short of the turning point b according to the movement of the plate 5, as shown in FIG. 4(C), a force F"h in the horizontal direction from the plate 5 at the point d is divided into a force component F"t is the tangetial direction of the sprocket and the other force component F"r in the radius direction of the sprocket, so that the drive pin 4 is rotated and moved by means of a moment produced by the force component F"t. Accordingly, the drive pin 4 reaches the turning point b passing through the point d.
However, a force F'h in the horizontal direction from the plate 5 is only applied to the drive pin 4 which is reached at the turning point b passing through the point c or d as shown in FIG. 4(B). Because the force component F't in the tangential direction of the sprocket against the force F'h becomes zero, the moment is not produced by the force component F't in the tangential direction of the sprocket and the drive pin 4 cannot be rotated and moved. Therefore, the drive pin 4 is stopped from moving at the turning point b on the sprocket 1 and locked.
The above problem also occurs at the turning point a of the sprocket 2.
When the drive pin 4 is locked so that the drive pin 4 is stopped from moving at the turning point a or b, the document table cannot be moved from the position where the drive pin 4 is locked. In the copying machine having the above document table reciprocating device, a lock releasing device must be additionally provided with the document table reciprocating device for releasing the locking of the drive pin 4, and can be manually operated.